A metered-dose inhaler consists of three major components; the canister which is produced in aluminium or stainless steel by means of deep drawing, where the formulation resides; the metering valve, which allows a metered quantity of the formulation to be dispensed with each actuation; and an actuator ( or mouthpiece ) which allows the patient to operate the device and directs the aerosol into the patient's lungs ., The formulation itself is made up of the drug, a liquefied gas propellant and, in many cases, stabilising excipients.
